The present invention resides in a novel system for obtaining information representative of the three-dimensional shape of an object in space and more particularly to a novel manner of developing projection patterns that can be projected onto the object each of which is imaged, the images then processed together in a certain way so as to measure the surface form of the object. It is especially important to the invention to be able to project a number of patterns having light and dark areas, the positioning of such areas in the different patterns being formed so as to have certain properties of the edges that are formed by and between adjacent light and dark areas in the different patterns, which correspond to projected surfaces in space, a major purpose of which certain properties is to maximize the number of such surfaces that can be projected while maintaining the ability to unambiguously identify each projected surface using only the sequence of images of the object. Profile lines or edges produced by different patterns will fall on the object to be reproduced. The pattern of the alternating light and dark areas is chosen to facilitate identification of these projected edges that fall on the object and are subsequently viewed and processed to measure the surface form of the object.
There are various systems for obtaining data useful to produce three-dimensional representations of an object. Such systems generally include a projector of radiant energy and a corresponding image recording means. The three-dimensional surface recording technology has grown substantially over the last several decades resulting in even more such systems. One such system, which like the one disclosed here and many others, dating back to early in the 20th century, e.g. Smith in U.S. Pat. No. 891,013, and Edmonds in U.S. Pat. Nos. 1,485,493, 1,615,261 and 1,716,768, and earlier by Willeme in U.S. Pat. No. 43,822, and more recently by Cruickshank, U.S. Pat. No. 4,613,234, and patent application Ser. No. 786,322, and Morioka in U.S. Pat. Nos. 3,580,758, 2,066,996, 2,350,796, 2,015,457 and 1,719,483; and in British Patent No. 439,448, as well as Jeffreys British Patent No. 471,617, comprises a camera-projector pair for the development of a data file which can be stored or used for subsequent representation of three-dimensional surface configurations, and is disclosed by DiMatteo et al in U.S. Pat. No. 3,866,052. With this and all such similar types of systems, the three-dimensional object to be recorded is placed in the field of projection of a light or other type of radiant energy projector, wherein the pattern of the projected light is structured in accord with the method of the particular invention. The surface of the object intersects with the projected light pattern in forming the reflected radiant energy. The radiant energy reflecting from the object is also within the field of view of the objective lens associated with a camera element. The geometric fixed relationship between the object, projector and camera lens is known and such information is subsequently employed together with the reflected radiant energy pattern in representating the surface configuration.
A concern of manufacturers and users of such systems is how to define a coordinate system which can be maintained and which facilitates the gathering of reliable data about the location and surface characteristics of the subject object; and from this information to identify with precision the spatial location of a point or series of points on the object's surface.
The approach claimed in U.S. Pat. No. 3,866,052 is well known in the prior art. See, for example, D. Calas, "Theory and Computer Implementation of Image Processing by Boolean Filters", Washington University of St. Louis Master's Thesis, 1970, as well as his references to preceding literature.
In light of the foregoing comments, it will be understood that a principal object of the present invention is to disclose a method of obtaining higher resolution three-dimensional representions of an object from fewer sequences of projections and recordings than is presently possible, and to obtain a given resolution with fewer projections and recordings. This also means that fewer projections and much less time is required by the present system to obtain data from which to gather information as to the shape of a surface contour. If the information is to be used in the reproduction of the shape of an object or person it means that the object or person needs to pose for a very short time, typically less than one second.
An additional object of the invention is to provide a method of digitizing data to enhance its interpretation and to produce a three dimensional representation of a surface.
Another object of the invention is to teach new and enhanced methods of profile line identification in the recorded image.
Another object is to locate, identify and develop data representative of profile edges projected onto an object and viewed by camera means.
Another object is to provide means to determine the location of points in space along a profile line projected onto an object and to produce data representative of said points in space.
A further object of the present invention is to provide a method of viewing, digitizing and processing of data to produce a quantitative measure of the viewed object.
A still further object of the present invention is to provide means of obtaining data useful to create an enhanced detailed representation of a viewed object without increasing the number of required mask segments.
Another object is to provide a three-dimensional representation means to enhance and ensure the accuracy of obtained data by systematically locating and identifying the location of profiles in a viewed image.
A further object is to obtain data corresponding to surface characteristics irrespective of the surface reflectance characteristics of the scanned object.
Yet a further object is to provide a novel method of accurately locating profiles using projected patterns and their functional inverses.
These and other objects and advantages of the present invention are realized by the present system which is based upon the light beam profiling principles described in John Cruickshank's portrait sculpture U.S. Pat. Nos. 3,796,129, 3,690,242 and 3,688,676. The basic concept disclosed in the Cruickshank patents is to recreate three-dimensional objects without requiring physical contact with the sensed object.
The method described in the Cruickshank patents utilizes the projection of a single planar surface, or sheet, light from a single projector to intersect the surface of the subject to be sensed; and a single photographic camera, positioned apart from the projector, to view and record an image of this light intersection, or "profile". In these patents it was shown that by knowing the positions and orientations of the projector and camera, as well as the focal length of the camera lens, the image of that profile can be projected onto a screen placed at a proper distance and angle from the projector to form a viewable image of a profile corresponding in size and shape to that created upon the original viewed surface. Through the process of moving the sensed surface and the projected light plane relative to one another, with or without concurrent movement of the camera as necessary, such profiles can be repeated at multiple positions over the surface so as to represent multiple profiles, which through a process of interpolation, can be used to represent the sensed surface. As disclosed in the Cruickshank patents, the system was used to manually trace the projected profiles so as to control a cutting machine to produce an approximate replica of the sensed object's surface.
The present system is an important improvement over the known prior art, including the Cruickshank patents. To generate a representation of part or all of a subject surface with the present system, spaced multiple light sheets produced by light sources including a laser light source are projected at the same time. Here, we include "light sheets" and "profiles" to be defined in the edge information between light and dark areas, that projected sheet or boundary forming a surface in space, intersecting in a line on the subject called a "profile". They intersect the subject giving it a zebra like appearance and are viewed together. With this system, instead of requiring N images to be processed for N profiles, multiple boundary surfaces are projected at once and only a smaller number of images need be viewed and processed to locate the resultant intersection profiles due to a novel technique for creating the patterns which uniquely identifies and corresponds the profiles in the viewed image with the projected surface that created them.
Once the imaged profiles are identified, if it is desired to sense more of the surface than is in common view between one projector of multiple surfaces and one camera, then the projector, subject, and camera, or any one or two of these, can be moved and the process repeated to obtain information about additional portions of the surface. The amounts of any such movement must be known quantitatively and employed in the solution. It is also contemplated to use a plurality of spaced stationary projectors and cameras, preferably in a darkroom, and to strobe the projectors in a sequence so that all or any desired surface portion of the object can be viewed and the data obtained processed to produce either a part or a full three-dimensional representation.
The projection patterns employed with the present system are uniquely designed in accordance with the present invention to facilitate identification and correspondence of the profiles in the viewed image with either the light sheets or the boundaries, or edges, between light and dark portions of the projected pattern. Briefly, the scheme is one of arranging light and dark banded areas on at least two projected patterns, such that they meet certain properties. One method of generating a set of patterns that meet these properties is described. In this example, each pattern correlates to a 16-bit long cyclic generatric code. Using this code as a basis, a much longer code is generated that has the desired properties of uniqueness throughout its length, and meets the chosen properties through out its length. By locating a profile in the viewed image, through a process of reading the code correspondng to the viewed image, the corresponding profile in the projected pattern can be identified, and the accuracy of the identification can be checked and if desired cross-checked.
The patterns also may be projected in the form of thin sheets of light rather than dark-to-light or light-to-dark boundaries or edges. This is done by projecting a pattern of thin light lines on a dark background, or vice versa.
The more boundaries or light sheets that are projected at once, the truer the resultant surface modeling. However, if they become too closely spaced, then optical and camera resolution may not separate them in the viewed image, thus losing the information carried by the denser profiles.
The exact spacing is also a subject of the present invention and is detailed in what follows herein. An important advantage is that, unlike previous methods, when using multiple patterns the projected surfaces are approxmiately evenly distributed among the multiple patterns, thus permitting the greatest number of profiles for a given number of patterns, concurrently permitting the greatest separation between profiles in any given image. Further, unlike previous methods, profiles need not repeat at the same place in more than one pattern. The importance of maximizing the separation between profiles in any one pattern is made clear in the following. The problems associated with dense profile packing are alleviated in the present invention by utilizing a series of patterns, which are normally projected and viewed in sequence but may also be projected and viewed simultaneously if the are made separable, such as through the use of different colors, polarigations, or combination thereof. In any one view, the profiles are sufficiently separated to resolve; and by interleaving these sets of pattern profiles any desired aggragate number of profiles can be obtained, at the expense of projecting and viewing a sequence of patterns. But the number of images for a given total number of profiles is relativley smaller than with methods of the earlier art. Further, the method provides uniquely identifiable profile lines, as will be explained. Since within a given image it is known which subset of the total number of profiles was projected, it is only necessary to identify the profiles within the respective subset for each given image. This in turn is made possible by using different spacings among the lines or edges in any one pattern, the spacings chosen to make a unique interleaving sequence among the patterns, this interleaving sequence either not being repeated throughout the pattern, or it repeated then providing additional identifiers to resolve them, thus permitting unique identification of all profiles by observing their sequencing with respect to all the patterns. This is one of the key features of the present invention. Further, in another embodiment, complementary additional patterns can be used to enhance the accuracy of locating a profile edge.
Instead of moving the projector, camera, or subject or a combination of these to sense more of the surface than is in view between one projector-camera pair, multiple stationary cameras and projectors can be used to observe more (or all) of the surface, thus requiring no motion.